Limit control device



Nov. 6, 1962 c. P. BURBEY ETAL 3,062,933

LIMIT CONTROL DEVICE 4 Sheets-Sheet 1 Filed Oct. 5. 1960 m H mHL 5 5 YmMM F. m? M HEM m MR4 m d 3 &# VJ

LIMIT CONTROL DEVICE 4 Sheets-Sheet 2 Filed Oct. 3, 1960 v m I m- HEP $1NM r &

Chas/er JOHFZOU IF z 3 INVENTORY P fiurbz/ BY ro/d A Mar-Me ATTORNEY!United States Patent Ofitice 3,062,933 Patented Nov. 6, 1962 3,062,933LIMIT CUNTKUL DEVICE Chester P. Burb'ey, Palo Alto, and Harold A.Marble, Burlingame, Calif assiguors to Tuck-Aire Furnace Company, SanFrancisco, Calif, a corporation of California Filed Oct. 3, 1960, Ser.No. 60,092 19 Claims. c1. zoo-81.9

This invention relates to a limit control device and more particularlyto a limit control device for use with furnaces.

This is a continuation-in-part of our application Serial No. 746,912,filed on July 7, 1958, now abandoned.

In the operation of gas furnaces, controls are provided to limit theoperating temperature of the furnace to a safe predeterminedtemperature. In counter flow furnaces, often two or more controls arerequired to satisfy American Gas Association and Underwriters Laboratoryrequirements. Onewof the controls is mounted in the upper part of thefurnace and is frequently called the upper limit control-and the otheris mounted in the lower part of the furnace and is oftencalled the lowerlimit control. The upper limit control prevents overheating of the upperpart of the furnace and turns off the gas supply. Overheating of thistype occurs if a fan or blower motor becomes jammed. It also can occurif the fan belt breaks. The lower limit control prevents air dischargedfrom the furnace from being overheated. Although the use of two suchcontrols is satisfactory, there is a need for a single control devicewhich will perform the functions of both of the conventional controls.Such a control device would appreciably reduce the initial cost and thecost of installation.

In general, it is an object of the present invention to provide a singlelimit control device which will perform the functions of twoconventional limit controls.

Another object of the invention is to provide a limit control device ofthe above character which is responsive to a moving air stream.

Another object of the invention is to provide a limit control device ofthe above character which is also responsive to temperature changes.

Another object of the invention is to provide a limit control device ofthe above character in which the sensitivity can be controlled.

Another object of the invention is to provide a limit control device ofthe above character which hasa wind operated reset.

Another object of the invention is to provide a limit control device ofthe above character which can be manually reset.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiments have been setforth in detail in conjunction with the accompanying drawings.

Referring to the drawing:

FIGURE 1 is a plan view of a limit control device embodying ourinvention;

FIGURE 2 is a front elevational view of the limit control switch shownin FIGURE 1;

FIGURE 3 is a partial front elevational view similar to FIGURE 1 with aportion of the wind vane broken away;

FIGURE 4 is a cross-sectional view taken along the line 4-4 of FIGURE 1;

FIGURE 5 is a cross-sectional taken along the line 5--5 of FIGURE 4;

FIGURE 6 is a cross-sectional view similar to FIG- URE 4 but showing thelimit control device with the switch in a closed position;

FIGURE 7 is an enlarged cross-sectional view taken along the line 7-,7ofFIGURE 4;

FIGURE 8 is a cross-sectional line 88 of FIGURE 7;

FIGURE 9 is a wiring diagram showing our limit control device connectedinto a conventional furnace;

FIGURE 10 is a plan view showing another embodiment of our limit controldevice;

FIGURE 11 is a plan view similar to FIGURE 10 but showing a portion ofthe wind vane cut away;

FIGURE 12 is a side elevational view partly in crosssection of the limitcontrol device shown in FIGURES 10 and 11;

FIGURE 13 is a cross-sectional side elevational view of still anotherembodiment of our limit control device; FIGURE 14 is a front elevationalview of the same;

FIGURE 15 is a cross-sectional view taken along the line 15-15 of FIGURE14;

FIGURE 16 is across-sectional view taken along the line 16-46 of FIGURE15; and

FIGURE 17 is a partial line 1717 of FIGURE 13.

In general, the limit control device consists of a switch movablebetween two positions with temperature responsive means for moving theswitch from one of the posi* tions to the other position. The devicealso includes view taken along the means responsive to airflow formoving said switch from' said other position to said one position toreset said switch.

The limit control device shown in FIGURES 19 of the drawing consists ofa housing 11 of suitable insulating material such as Bakelite and amounting plate 12 to which the housing is secured by suitable means suchas screws 13. An elongate framework has its front end fixed to themounting plate 12. As shown, the framework 14 is substantially U-shapedin cross-section and is tapered toward the rear. The framework isprovided with openings 16 in its lower portion for a purpose hereinafterdescribed.

A snap-acting switch 17 is mounted within the housing 11 and consists ofstationary contacts 18 and a movable contact member 19 carrying a pairof contacts 21 which are adapted to contact or engage the stationarycontacts 18. The contact member is provided with a pair of earlikeportions 22 which are rockably seated on one end of a contact carryingmember 23. The contact carrying member 23 is pivotally mounted between apair of posts 24aftixed to the housing 11 by suitable means such as thescrew '26. A spring 27 has one end secured to an extension 28 of thecontact carrying member 23, and the other end is secured to a' link 29which is secured to a post 31 afiixed to the housing 11.

From the construction described, it is readily apparent that as the endof the contact carrying member 23 to which the spring 27 is securedpasses through center, the switch will be moved rapidly toward a closedposition or an open position, depending upon the direction of movementof the member 23 to prevent excessive arcing of the contacts.

An operating arm 32 is mounted on the contact carrying member 23 andextends generally in the same direction as the contact carrying member.The operating arm 32 is adapted to be moved by a manual reset button 33.The manual reset button 33 is provided with a plunger 34 which is fixedto the extreme end of the operating arm 32. Thus, it is apparent whenthe reset button 33 is moved inwardly, the contacts of the switch aremoved toward a closed position.

An adjusting screw 36 is threaded into the housing and is adapted to bepositioned so that it will be engaged by the operating arm 32 for apurpose hereinafter described.

An additional operating arm 37 has one end mounted on the contactcarrying member 23 at right angles to the operating arm 32 and extendsrearwardly through a slot 38 in the mounting plate 12. The operating arm37 explan view looking along the tends rearwardly for a substantialdistance into the framework 14. The operating arm 37 is adapted to beengaged by temperature responsive means 39 and wind responsive means 41.

The temperature responsive means consists of a lever 43 which has oneend pivotally connected to the framework 14 at 44. The other end of thelever is threadably engaged by a screw 46 by which the positioning ofthat end of the lever can be controlled relative to the framework 14. Acoil spring 47 is mounted on the screw 46 and ensures that the screwfirmly grips the lever 43. The lever 43 is provided with openings 43 fora purpose hereinafter described.

An operating lever 49 is pivotally mounted on the lever 43 at 51 and hasa portion 52 which is adapted to engage the operating arm 37. The otherend of the operating lever 49 is provided with a forked construction 53in which upper forked portions 53a and 53b are adapted to engage theupper surface of one end of a bimetallic element 54 and in which a lowerforked portion 590 is adapted to engage the lower surface of the sameend of the bimetallic element. The other end of the bimetallic elementis affixed to the end of the lever 43 at 56.

The wind responsive means 41 consists of a wind vane 58 which has asubstantially planar upper surface 59. Suitable means is provided forattaching the vane to the operating arm 37 and, as shown, consists of aportion 61 of the vane which is bent downwardly and which is providedwith a slit 62 which is adapted to receive the operating arm 37. Theportion 61 also seats in a notch 63 provided in the operating arm. Theother end of the vane is also provided with a portion 64 which is bentdownwardly and engages the operating arm 37 is a suitable manner. Forexample, as shown, the portion 64 can also be bent inwardly to engage aslit 65 in the operating arm 37.

A typical wiring diagram showing the use of one of our limit controldevices is shown in FIGURE 9. As shown, the limit control device 67 isconnected to line voltage in series with a room thermostat 68, asolenoid operated gas valve 69 and a safety pilot device 71.

Operation of our limit control device may now be briefly described asfollows: Let it be assumed that our limit control device has beeninstalled in a counter-flow furnace in the path of air flow andconnected as shown in the wiring diagram in FIGURE 9. Let it also beassumed that the furnace is operating properly and that the snap-actingswitch is in closed position as shown in FlGURE 6 of the drawing. Nowlet it be assumed that the outlet air from the furnace becomesoverheated for some reason, such as all the outlet ducts from thefurnace being closed. As the furnace heats up, the hot air will passthrough the openings 16 and 48 and over the bimetallic element 54 tocause it to heat up. As the bimetallic element heats up, the end of thebimetallic element engaging the forked portions of the operating lever49 will be moved downwardly, as viewed in FIG- URE 6, to urge the otherend of the lever 49 into engagement with the operating arm 37. When thepredetermined temperature, for which the control device is set, isreached, the bimetallic element through the lever 49 will cause theoperating arm 37 to be lifted which will cause opening of the contactsof the switch 17.

It will be noted that upward movement of the operating arm 37 carrieswith it the vane 58. As soon as the furnace starts cooling, theoperating lever 49 moves out of engagement with the operating arm 37.The operating arm 49 cannot cause resetting of the switch 17 because itcannot engage the arm on downward travel. However, as soon as the lever49 moves out of engagement with the operating arm 37, the pressure ofthe wind or air against the vane 58 will cause downward movement of thevane and the operating arm 37 to reset or close the contacts of theswitch 17. Thus, it can be said that the vane 58 serves as air-operatedreset means,

In the case of a power failure, there often is enough residual heat inthe furnace to cause operation of the bimetallic element and opening ofthe contacts. Normally this would require that the switch be manuallyreset. However, with our switch, the switch will be reset automaticallyas soon as the blower starts operating. As is well known in manyfurnaces, the burner must be turned on and burn until a predeterminedtemperature is reached in the furnace before the fan or blower will beturned on.

If the temperature in the furnace rises for some other reason, such as,for example, if the fan belt breaks or the blower motor becomes jammed,the switch 17 will be opened in the same manner when the temperaturewithin the furnace rises above a predetermined temperature. However, inthis case, the switch 17 will not be automatically reset by the vane 53because no air or Wind is passing through the furnace and over the vane58.

Before the control device will automatically reset, the damage ormalfunctioning component in the furnace must be repaired. The switchcan, however, be manually reset by operating the manual reset button 33.

The temperature at which the bimetallic element 54 will cause opening ofthe contacts of the switch 17 is adjusted by the screw 46 by raising orlowering the lever 43.

The adjustment screw 36 is utilized to increase or decrease the pressurerequired on the wind vane 58 to reset the switch 17. Thus, as the screw36 is moved inwardly to limit the amount of movement of the operatingarm 32, the contact carrying member 23 will be moved closer to the pointat which snap action occurs. For that reason, less pressure will berequired on the operating arm 37 to move the switch to the closedposition. The position of the screw as .does not affect the sensitivityor operation of the temperature responsive means 39.

Another embodiment of the invention is shown in FIG- URES 10, ll and 12.This embodiment of our invention is very similar to the embodimenthereinbefore described except for the differences in the operating arm37 and the Wind responsive means 41. As shown, a relatively shortoperating arm 74 is provided which is adapted to be engaged by theportion 52 of the operating lever 49. The operating arm 74 is adapted tobe engaged by wind responsive means 76 which consists of a wind vane 77which has upwardly inclined side edges 78 and 79. The rear end of thevane is pivoted to the framework 14 at 81 and is provided with adownwardly turned portion 82 at its forward end which rests upon theoperating arm 74. The operation of this embodiment is similar to thathereinbefore described. When the snap-acting switch 17 is opened by thetemperature responsive means 39, the switch will be automatically resetby the wind or air acting upon the wind vane 77. Pressure on the windvane will urge the operating arm downwardly to close the contacts of theswitch.

Another embodiment of our invention is shown in FIGURES 13 through 17 Ascan be seen from the drawings, it is similar to the embodimentshereinbefore described. It consists of a Bakelite housing 86 secured toa metal plate 87 by screws 88. An elongated framework 89 very similar tothe framework 14 has its front end secured to the metal plate 87.Openings 91 are provided to facilitate air flow through the limitcontrol device as hereinafter described.

A snap-acting switch 92 is mounted within the housing 86 and consists ofa pair of stationary contacts mounted in the housing and which areprovided with screws 94 to facilitate attachment of leads or wires tothe stationary contacts. A movable contact member 96 is movable into andout of engagement with the stationary contacts and when in engagementwith the stationary contacts serves to form an electrical connectionbetween the stationary contacts. The movable contact member 96 isprovided with cars 97 which are loosely mounted in recesses 98 providedon opposite sides of a mounting member 99. A leaf spring member 101 isprovided which has ears 102 which also extend into the recesses 98. Theleaf spring member underlies the U-shaped mounting member 99 as shownparticularly in FIGURE 16. The leaf spring member 101 is provided withan in-turned central portion 103 which seats in an indentation 104provided in the contact member 96. The inturned portion 103 thereforeserves to generally position the contact member 96. The U-shapedmounting member is provided with lugs which are pivotally mounted on astationary member 107. The stationary member 107 has ears 108 which arefixed in slots provided in vertical posts 109.

The mounting member 99 is provided with an extension 1 11 which carriesone end of a spring 112. The other end of the spring 112 is connected toa link 113 carried by a post 114. An arm 116 of suitable insulatingmaterial is fixed to the mounting member 99 by rivets 116 and extendsupwardly in the same general direction as the mounting member. The freeend of the arm 116 is provided with a member 117 which 118.

A reset pin 121 is loosely mounted in a collar-like member 122 to permitpivotal movement of the reset pin 121 for a purpose hereinfaterdescribed. An abutment member 123 is mounted on the reset pin and isprovided with a shoulder 124 which is adapted to engage the flange "118of the member 117 as shown particularly in FIGURE 15. And is also shownin FIGURE 15, the reset pin extends through an opening 126 provided inthe plate 87 and overlies the framework 89 for a purpose hereinafterdescribed.

An operating arm 128 of suitable insulating material is secured to oneside of the mounting member by suitable means such as the rivets 129 andextends through an opening 131 in the plate 87. The operating arm 128 isadapted to be engaged by temperature responsive means 131 whereas thereset pin 121 is adapted to be engaged by wind responsive means 132.

The temperature responsive means 131 is substantially identical to thetemperature responsive means 131 hereinbefore described, and consists ofa lever 133 pivotally connected to the framework 89 at 134. The otherend of the lever is threadably engaged by a screw 136 to permit verticaladjustment of the lever. A spring 137 maintains firm engagement betweenthe screw 136 and the lever 133. Openings 138 are provided in the leverarm and are in general registration with the openings 91 in theframework 89. An operating lever 141 is pivotally connected to theframework 89 at 142 and has one end portion 143 which is disposed in aslot 144 provided in the operating arm 128. The other end of theoperating lever 141 is provided with a forked portion 146 which forms arecess 147 which receives one end of a suitable temperature sensitiveelement 148 such as a bimetallic element. The other end of thebimetallic element is fixed to the lever 133 by suitable means such asrivets 151.

The wind responsive means 132 consists of a wind vane 156 providing aflat surface which lies generally in a horizontal plane when the switchis in its normal position as shown in FIGURE 13. The vane 156 ispivotally mounted to the framework 89 at 157. The vane is provided withtwo extending arm portions 158 which carry a cylindrical counterweight159. One of the arms 158 carries an operating extension 161 which isadapted to engage the reset pin 121 as shown particularly in FIGURES 13and 15. As will be noted particularly from FIGURE 17, the vane 156 hassuch a width that it is slightly less than the width of the U-shapedmember 89. However, the vane 156 is provided with an end portion 163 ofsubstantially greater width than the other portions of the vane so thatthe vane cannot drop below the upper edges of the U-shaped framework 89.This carries a flange 6 portion of increased area makes the device moresensitive because of the lever arm advantage.

Operation of this embodiment of our limit control device may now bebriefly described as follows: Let it be assumed that the limit controlswitch has been installed in a counter-flow furnace so that it ismounted in a vertical position with the wind vane 136 being in asubstantially horizontal position. When the furnace is operatingproperly, the switch 92 will be closed and the wind vane 156 will be inengagement with the U-shaped frame and will be lifting the inner end ofthe reset pin 121 upwardly. Now let it be assumed that for some reason,the outlet air from the furnace reaches a temperature above apredetermined safe temperature. When this occurs the air flowing throughopenings 91 and 138 will cause the bimetallic element 148 to heat up andwill cause its free end to move downwardly to cause movement of theoperating lever 141 and upward movement of the operating lever 128 toopen the switch 92. As will be noted from FIGURE 13 this opening of theswitch 92 is not effected by the Wind operated means 132. However, assoon as the switch 92 is opened, the furnace is shut down and the windvane moves to the position shown in FIGURE 13 because of the weight ofthe counter-weight 159. The reset pin is therefore permitted to dropdown so that the shoulder 124 comes into engagement with the flange 118to hold the switch 92 in the open position as shown in FIGURES 15 and16.

As soon as the furnace cools, the operating lever 141 will attempt tomove downwardly. However, the switch 92 cannot be moved to the closedposition until the reset pin 121 is actuated to release the flange 118.

If the control is such that the fan does not cease operating uponoverheating of the furnace, the vane 156 will maintain the reset pin outof engagement out of the flange 118 and therefore the switch 92 can beclosed as soon as the bimetallic element 148 cools below thepredetermined safe temperature.

As the temperature in the furnace rises because something has happenedto the blower and no air is passing through the furnace, the wind vanewill move to the position shown in FIGURE 13 and will permit the resetpin to come into engagement with the flange 118 when the switch 92 isopened by the bimetallic element 148 because of overheating of thefurnace.

As soon as the air flow is resumed through the furnace, the windoperated means 132 will release the reset pin 121 to permit the switch92 to be moved to the closed position.

Our limit control device has been found to operate very satisfactorilybecause very little pressure is required to raise the inner end of thereset button to release the flange 118. The reset pin is mounted in thehousing 86 in such a manner that the switch can be reset manually whendesired. However, before the limit control device resets itselfautomatically there must be air flow through the furnace and thetemperature of the air through the furnace must be below a predeterminedsafe temperature.

The arrangement of the switch 92 is such that snap action is obtainedwhen the switch is moved between open and closed positions. Thetemperatures at which the bimetallic element 148 causes opening orclosing of the switch 128 is adjustable by adjustment of the screw 136.The reset pin 121 is always in a position to engage the flange 118. Theswitch is mounted in such a manner that the inner end of the reset pinis pulled downwardly by the force of gravity about the pivot pointprovided by the collar 122. The pin is relatively small so that it canbe raised readily by the wind op erated means to facilitate automaticresetting of the limit control device.

It is apparent from the foregoing that we have provided a new andimproved limit control switch which is particularly adapted for use incounter-flow furnaces and which can be utilized to take the place of twoor more conventional switches. The reset which is responsive to air flowis particularly advantageous in that it eliminates the use of anadditional switch which is normally required to detect malfunctioning ofthe fan or blower. The limit control device is extremely sensitive tohigh rates of temperature change and is readily adjusted and installed.

It is also apparent from the foregoing that instead of a wind operatedreset, that an air pressure operated reset can be utilized to accomplishthe same purpose. The blower in the furnace by creating an air flow alsocreates a differential in pressure between the interior of the furnaceand normal atmospheric pressure. This pressure diiierential can be usedto operate a diaphragmlike device or similar device to reset the switchand thereby accomplish the same results as the wind operated reset.

We claim:

1. In a limit control device, a switch movable between two positions, anoperating arm, manual reset means adapted to engage said operating armto move said switch from an open to a closed position, an additionaloperating arm mounted on said switch, temperature responsive meansincluding a bimetallic element adapted to engage said additionaloperating arm for moving said switch from a closed to an open position,and wind responsive means operatively connected to said operating arm tomove said switch from an open to a closed position.

2. A limit control device as in claim 1, together with means foradjusting the amount of wind pressure required to cause movement of theswitch from an open to a closed position, said adjustment meanscomprising means adapted to engage said first named operating arm toprevent movement of said operating arm beyond a predetermined position,and to increase the sensitivity of the operating arm to air movement.

3. In a limit control device, a housing, a switch mounted in saidhousing and movable between open and closed positions, an operating armmounted on said switch and extending through said housing, a frameworkmounted On said housing, temperature responsive means including abimetallic element carried by said framework and adapted to engage saidoperating arm to move said switch from a closed to an open position, andwind responsive means including a vane adapted to be engaged by the windfor controlling the movement of said switch from an open to a closedposition.

4. A limit control device as in claim 3 wherein said vane is mountedsolely on said operating arm.

5. A limit control device as in claim 3 wherein said vane has one endpivotally mounted on the framework and has the other end engaging theoperating arm.

6. In a limit control device, a switch movable between open and closedpositions, an operating arm secured to said switch for moving saidswitch from one of said positions to the other of said positions,temperature responsive means including a bimetallic element engagingsaid operating aim for operating said switch, and wind responsive meansincluding a vane adapted to be engaged by the wind for controlling themovement of said operating arm.

7. In a limit control device, a housing, a switch mounted in saidhousing and movable between open and closed positions, an operating armmounted on said switch and extending through said housing, a frameworksecured to the housing, an additional operating lever pivotally mountedin said framework and having one end engaging said operating arm, abimetallic element having one end secured to said framework and havingthe other end engaging said operating lever, and wind responsive meansincluding a vane adapted to be engaged by the wind for controlling themovement of said first named operating arm.

8. A limit control device as in claim 7 wherein said S additionaloperating arm and said bimetallic element are substantially in axialalignment.

9. In a limit control device, a housing, a switch mounted in saidhousing and movable between open and closed positions, an operating armmounted on said switch and extending through said housing, a frameworkmounted on said housing, an operating lever pivotally mounted in saidframework and having one end engaging said operating arm and adapted tomove said first named operating arm to move said switch from a closed toan open position, a bimetallic element having one end secured to saidframework and having the other end engaging said operating lever, andwind responsive means including a vane adapted to be engaged by the windfor controlling the movement of said switch from an open to a closedposition.

10. In a limit control device, a switch movable between first and secondpositions, an operating arm secured to said switch, temperatureresponsive means including a bimetallic element engaging said operatingarm for moving said switch from said first position to said secondposition, and wind responsive means controlling the movement of saidswitch from said second position to said first position.

11. In a limit control device, a housing, a switch mounted in saidhousing and movable between first and second positions, an operating armmounted on said switch and extending through said housing, an additionaloperating lever pivotally mounted in said framework and having one endengaging said operating arm, a bimetallic element having one end securedto said framework and having the other end engaging said operatinglever, said bimetallic element serving to move said switch between saidfirst and second positions, and wind responsive means controlling themovement of said switch from said second position to said firstposition.

12. In a limit control device, a switch movable between first and secondpositions, an operating arm secured to said switch, temperatureresponsive means engaging said operating arm and moving said switchbetween said first and second positions, reset means adapted to locksaid switch in one of said positions and wind responsive means forautomatically releasing said reset means to permit the control of saidswitch to be returned to said temperature responsive means.

13. A limit control device as in claim 12 wherein said reset meansincludes a member continuously and yieldably urged into an engagingposition.

14. A limit control device as in claim 13 wherein reset means can beoperated manually to reset the switch.

15. In a limit control device, a housing, a switch mounted in saidhousing and movable between open and closed positions, an operating armmounted on said switch for operating the same and extending through saidhousing, a frameword mounted on said housing, an operating leverpivotally mounted in said framework and having one end engaging saidoperating arm, a bimetallic element having one end secured to saidframework and the other end engaging said operating lever for moving theswitch between said first and second positions, reset means mounted inthe housing and adapted to engage said switch to maintain said switch inone of said first and second positions, and wind responsive means forreleasing said reset means.

16. A limit control device as in claim 15 wherein said reset means isprovided with means to permit manual operation of the reset means toreset the switch.

17. A limit control device as in claim 15 wherein said wind responsivemeans is provided with a counter weight to normally maintain said windresponsive means out of engagement with the reset means when the wind isnot impinging upon the wind responsive means.

18. A limit control device as in claim 16 wherein said reset meansincludes a pin pivotally mounted in said housing and means yieldablyurging said pin into engagement with said switch.

1,9. A limit control device as in claim 16 wherein said References Citedin the file of this patent reset means includes an arm secured to saidswitch, a pin UNITED STATES PATENTS pivotally mounted in said housingand normally urged downwardly by gravity, and an abutment member carried2,518,176 Powers 81 1950 by the pin and having a shoulder adapted toengage the 5 2,348,167 Matthflws 1958 arm carried by the switch.,848,582 Booth Aug. 19, 1958

